1. Field of the Invention
The present invention relates to a photosensitive resin composition, and more particularly to a photosensitive resin composition excellent in properties such as flexibility and impact resilience, which is less affected by humidity.
2. Description of the Prior Art
In the past, a photosensitive resin composition (hereinafter, referred to as a composition) comprising as basic components a soluble synthetic polymer, a photopolymerizable unsaturated compound, and a photopolymerization initiator has widely been used in the fields such as relief plates for various kinds of printing, relief masks for sand blasting, design and pattern for decoration, photo resists, displays, name plates, photoadhesives, photo-curable paints, UV-curable inks, ion exchange resins (films), selective transmission films, and stabilization enzyme films. For example, a relief plate is usually manufactured as follows: First, an original plate including a support on which a photosensitive resin composition layer is formed is exposed to light through a negative film or a positive film, whereby the photosensitive resin composition on the exposed portion is optically hardened and insolubilized. Then, the photosensitive resin composition which is not exposed to light is dissolved in an appropriate solvent and removed, thereby obtaining a relief plate. Among the above-mentioned components, properties of a soluble synthetic polymer are important. When the soluble synthetic polymer is used for a relief plate, the following requirements should be satisfied.
(1) The soluble synthetic polymer is soluble in an appropriate solvent.
(2) The surface of a composition layer formed on a support is contacted with a negative film for exposure to light and the photopolymerizable unsaturated compound on the exposed portion is photopolymerized and insolubilized.
(3) A relief plate obtained is excellent in transparency, abrasion resistance (printing resistance) and solvent resistance (ink solvent resistance).
Polyamides have been used as a soluble synthetic polymer which satisfies the above-mentioned requirements. In recent years, because of diversified uses of printing, there is a great demand for a wide variety of relief plates ranging from a high-hardness plate of about 80.degree. in Shore D to a super-softness plate with impact resilience and with flexibility of about 40.degree. in Shore A. In particular, impact resilience has become important in order to obtain stable printed matters when high speed printing is performed. Accordingly, flexibility and impact resilience have been required for soluble synthetic polymers.
As a soluble synthetic polymer which satisfies the above requirements, an addition polymer obtained by the reaction between a diamine compound having at least one amide bond and an organic diisocyanate compound has been proposed (Japanese Laid-Open Patent Publication No. 58-140737). This addition polymer is obtained by the addition-polymerization of the diamine compound which is a hard segment with an organic diisocyanate compound containing as a soft segment polyoxyalkylene glycol. Since this addition polymer is an elastomer having a block structure consisting of a hard segment and a soft segment, a relief plate obtained by using a composition comprising this addition polymer is excellent in flexibility and impact resilience. However, in the relief plate obtained by using a composition comprising this addition polymer, impact resilience is likely to change depending upon humidity. That is, the impact resilience is highly dependant on humidity. Thus, there is a problem in that when such a relief plate is used for printing, especially at high speed, stable printed matters cannot be obtained.